Two-dimensional infrared correlation analysis of electrochemical reactions

Three advanced IR spectroscopy techniques, surface-enhanced IR absorption spectroscopy (SEIRAS), step-scan Fourier-transform interferometry, and two-dimensional (2D) IR correlation analysis, have been applied to the study of electrochemical reactions. A combined use of SEIRAS and step-scan interferometry enables time-resolved spectral monitoring of electrochemical reactions with time-resolutions ranging from microseconds to milliseconds. 2D-IR correlation analysis highlights the dynamic information obscured in the time-resolved spectra, The basic concept of 2D-IR is somewhat analogous to that of 2D-NMR, and synchronous and asynchronous 2D spectra defined by two independent wavenumbers are generated by a correlation analysis of dynamic fluctuation of IR signals induced by a potential modulation, The synchronous and asynchronous spectra characterize the coherence and incoherence respectively of dynamic fluctuations of IR signals at two different wavenumbers. Bands arising from different transient species are clearly differentiated by their characteristic time-dependent behavior, The temporal relationship between the intensity fluctuations of different bands also becomes clear. From these data, deep insights into reaction processes are gained. The utilities of 2D-IR are demonstrated for the one-electron reduction of heptylviologen at a silver electrode surface. (C) 1997 Elsevier Science S.A.